1. Field of the Invention
The present invention generally relates to a facsimile system for electrically transmitting document data and more particularly to document reading apparatus, facsimile equipment and LSI circuits suited for processing multi-colour document data.
2. Description of the Related Art
A system for reading colour pictures by using a plurality of light sources having different spectral characteristics has already been proposed, as disclosed in No. JP-A-59-189775. Also, a colour picture reading system has been proposed in which at least one of the light sources is continuously energized throughout the entire period during a reading operation is performed.
In a two-colour facsimile system typical of multi-colour facsimiles known heretofore, transmission schemes differ from one to another depending on the manufacturer because the standards therefor have not yet been established.
There is also known a shading correction system in which a standard or reference sheet for colour detection or identification is made use of, as described in No. JP-A-61-74447.
Further, a distortion correcting LSI circuit has also been proposed, as disclosed in No. JP-A-60-94576.
It is noted, however, that in the colour document reading apparatus of the prior art, no consideration has been made of the fact that a plurality of light sources having different spectral characteristics exhibit different behaviours with respect to variation in the quantity of light emitted over time as well as in dependence on temperature, thus giving rise to a problem in that erroneous colour identification might undesirably be made due to erroneous operation of a colour separation circuit.
Also, in the multi-colour facsimile systems known heretofore, no measures have been taken concerning the possibility of distinction between different colours by displaying them with correspondingly different monochromatic patterns such as black and white patterns, as required in the case of communication with the conventional monochromatic G2, G3 or G4 facsimiles. Consequently, transmission of multi-colour document data is possible only with multi-colour facsimile apparatus equipped with a multi-colour recording apparatus and is very inconvenient.
It is further noted that the distortion correcting circuit of the prior art requires a relatively large number of peripheral circuits because the distortion correcting LSI for a monochromatic facsimile is employed.
According to the prior art distortion correcting method, a reference signal for correction has to be inputted before the document is read. Consequently, control can not follow up changes in the distortion characteristics taking place in the course of reading a document, thus presenting a further problem.